Helicopter rotor blade

ABSTRACT

A HELICOPER BLADE COMPRISING A PLURALITY OF BONDED COMPONENTS FORMING A UNITARY STRUCTURE HAVING A LONGITUDINALLY EXTENDING PORTION, A GRADUAL TRANSITIONAL PORTION AND A HOLLOW TUBE-LIKE PORTION. THE HOLLOW ROOT PORTION OF THE BLADE IS SECURED TO A ROTOR.

July 4, 1972 G. MONTI 3,674,379

HELICOPTER ROTOR BLADE Filed Jan. 2e, 1970 INVENTOR @M1/amm MOA/Tl KGEUTUnited States Patent O HELICOPTER ROTOR BLADE Giancarlo Monti, Varese,Italy, assignor to Siai-Marchetti S.p.A., Varese, Italy Filed Jan. 26,1970, Ser. No. 5,886 Claims priority, application Italy, Jan. 30, 1969,12,171/69 Int. Cl. B64c 27/48 U.S. Cl. 416-226 4 Claims ABSTRACT OF THEDISCLOSURE A helicopter blade comprising a plurality of bondedcomponents forming a unitary structure having a longitudinally extendingportion, a gradual transitional portion and a hollow tube-like portion.The hollow root portion of the blade is secured to a rotor.

The present invention relates to an improved blade for the main rotor ofa helicopter or like craft.

As is well known, the rotor blades of helicopters are stressed byconsiderable oscillatory loads. At present, the material of which suchblades are made, while being capable of withstanding high static loads,resist only low oscillatory loads which must, therefore, be kept low ifthe blade is to have a long life. Moreover, particular care must bedevoted to the prevention of stress concentrations, sharp changes ofcross-sectional configuration and the like, all of which tend to reducethe life of the blade components. Rotor blades are presently made ofdifferent materials, such as wood, metals and plastics, and usually areconnected with their yoke by a system including a separable grip member,a bolt and a drag brace. The grip is supported on the yoke by means offeathering bearings, permitting the blade to be turned to allow theadjustment of the blade pitch. Opposed blades are connected with eachother by a strap and bolt.

A drawback of the above system is that a concentration of stressesoccurs in a number of points, as e.g. in the eye or mountings of thebolt and in the eyes of the drag brace. To withstand such concentratedfatigue stresses, the sections are increased in mass or size whichresults in substantial localized increases in the stiffness of the bladeand of the grip. Thus, the sectional modulus and inertial momentdistributed along the blade span does not change gradually but in adiscontinuous manner. Such discontinuities in the structure and in thestiffness of the blade lead to local increases in the oscillatingstresses.

Other drawbacks are apparent from procedure presently followed in themaking of blades for helicopter rotors, as explained hereinbelow.

(a) Wooden blades: Such blades are suitable for small helicopters onlysince when the rotor sizes are increased, the weight of wooden bladesbecome disproportionately great (i.e. the weight increases proportionalto the cube of rotor diameter), and thus extremely heavy blades would berequired for large diameter rotors. Moreover, much labor is required inthe making of such blades although, conversely, the required equipmentis relatively less expensive. Thus, wooden blades are acceptable for asmall range of sizes and where mass production does not raise the coststoo high. Moreover, a relatively low stiffness is shown by the woodenblades, as a consequence of the low modulus of elasticity of wood. Thepresent ice trend is conversely directed towards the production ofhighly stiff blades, capable to better withstand the aerodynamic anddynamic loads of modern high capacity, powerful helicopters. Finally,the wooden blades, being made of a highly hygroscopic material, undergoan increase in weight, caused by the gradual absorption of air moisture,resulting in deformations which cause difficulties in the balancing ofrotors and excessive vibrations.

(b) Metal blades: Presently, nearly all helicopters are equipped withmetal blades. The advantages of such blades consist in a rigidity muchgreater than that of wooden blades, and in the non-hygroscopicity oftheir material so that they do not suffer from the effects of humidity.To decrease the blade weight to an acceptable limit, metallic blades aremade of a load carrying rib structure, covered with thin sheets of analuminum alloy (usually .016" thick). However, such thin gauge sheetseasily suffer from corrosion problems, by which the life of a blade maybe significantly decreased. Indeed, when corrosions are noticed on thesurface, the tendency is to have the corroded areas polished. However,only a limited number of such polishing operations can be made if anexcessive decrease in the thickness of the sheet is to be avoided. Onthe other hand, the corroded surfaces must be polished, both to keep thecorrosion from spreading and to prevent the surface from pinholding.

(c) Plastic blades: A number of manufacturers have recently startedproduction of blades for main rotors consisting of structures made offiberglass fabric impregnated with plastics, such as epoxy resins or thelike. Such blades show the advantages of being non-hygroscopic, unlikethe wooden blades, and do not require very thin coverings like the thingauge metal sheets which esaily undergo corrosion. However, seriousdifficulties are encountered in the formation of connecting points,joints or bearing surfaces, as e.g. the feathering bearing housing orthe blade root by which the blade is connected to the grip. Moreover,present experience in this field is yet insufficient to know thebehavior of such blades under a fatigue stress caused by aging under theaction of atmospheric agent (sudden changes of temperature, effects ofUV radiations, etc.).

The drawbacks of these conventional blades are avoided by the blade madeaccording to the invention, which also shows, as an added advantage, agradual variation, without abrupt changes, of the inertial and sectionalspanwise modulus.

According to the invention, the blade comprises a plurality oflongitudinally arranged components, fitted side by side and crosswisesecured to each other, these components being preferably symmetricallylocated with respect to the longitudinal cross-sectional axis.

As will be described more fully later, the blade may be formed of afirst component made of an aluminum alloy in a range of at least 0.118"to 0.157 thick, located to form the leading edge of the blade anddesigned to act as the main load bearing structure and comprising alsothe root of the blade; a second component of at least one honeycombstructure preferably of plastic, and with inner cavities, by which thecontinuity of the blade shape is ensured; a third component consistingof a honeycomb filling, preferably of plastic, and finally a fourthmetal component, preferably of aluminum alloy, representing the trailingedge, by which the shape is defined and which contributes, at leastpartly, to the strength of the assembly,

the last component being connected at the root of the blade with thefirst metal component.

The above components are connected with each other by any conventionalbonding process, e.g. by having a film of adhesive, such as theforementioned epoxy resin, interposed between the components, whereafterthe assembly may be cured according to the selected adhesive.

The assembly of different components of which the blade is made up, maythen be covered with a continuous sheet made of plastic material, alsobonded to the inner components along the whole contact surface.

Therefore, the blade according to the invention will not be exposed tothe risk of corrosion, except for the metal components of the leadingand trailing edges which, however, being relatively thick, may besubmitted to a large number of polishing treatments.

'I'he above and further features of the invention will be betterappreciated from a consideration of the following detailed descriptionof the invention, which is shown as an illustrative embodiment in theaccompanying drawing wherein:

FIG. 1 shows a hub for helicopters with the related connection and ablade of the conventional prior art design.

FIG. 2 shows a blade made according to the present invention, partlysectioned near the root, and

FIG. 3 is a cross-section of the blade, taken on the line III-III ofFIG. 2.

The prior art construction shown in FIG. l comprises at least one pairof opposed 'blades 1, secured to a grip 2 by means of a bolt 3 and adrag brace 4. The grip 2 is supported on the yoke 5 of the rotor hub bya plurality of feather bearings 6 which allow the adjustment of theblade pitch by rotation of the grip. The opposed blades are connected toeach other by a strap 7 fixed at each end by a bolt 8 through the grip2. lt will thus be apparent how the concentration of stresses mentionedearlier can occur and how these prior art blade constructions aresubject to numerous disadvantages.

The blade of the present invention is seen in FIGS. 2 and 3. Only oneblade is seen, and only a part of the rotor and hub is shown. Except forthe construction of the novel blade, the rotor, feather bearings, etc.,remain the same as in FIG. 1.

Referring now to FIGS. 2 and 3, the yoke 5, as shown therein, issubstantially similar to the conventional yokes for main rotors, asshown in FIG. 1. Fitted on the yoke 5 are the feathering bearings 6, bywhich rotation about the longitudinal axis of the blade is allowed, foradjustment of pitch. Also shown is a strap 7 by which the two oppositeblades are connected with one another with the aid of a bolt 8 that isthreaded through the root of the blade.

The blade according to the invention comprises a first longitudinalmetal rib component 9, preferably made of an aluminum alloy, extendingspanwise and acting as main load bearing structure. Integral with therib component 9 and smoothly extending therefrom is the root 9a.Feathering bearings 6 and the bolt 8 for the strap 7 are accommodated inroot housing 9a. It is seen that the first member forms a unitaryleading edge and root having smooth surface transitional sections.

As shown in FIG. 3, the one-piece rib component 9 has a substantial wallthickness, and is preferably formed as a singular hollow tubular unitwith an inner partition wall 9b, acting as resisting and stiffeningelement. The wall thickness ranges between 0.110" and 0.157.

Bonded to component 9 is a component 10 consisting of a lightweighthoneycomb panel, preferably of plastic, and having large inner cavities.The task of the component 9 is to ensure the continuity of the shape ofthe leading edge and to provide an airfoil surface bonded to a fillingelement 11 also made of lightweight expanded or honeycomb plastic, butwithout inner cavities. This element is in turn bonded to a secondelongated metal component l2, preferably made of an aluminum alloysimilar' to 4 that of leading edge 9. The second metallic component 12defines the trailing edge of the blade.

As shown in FIG. 2, the metal trailing edge 12 is connected, at itsroot, with the metal rib structure 9.

5 The whole bladeexcept for a part of metal leading edge 9-is covered bya fabric 13 consisting of plastic fibers. The whole assembly ofcomponents and covering sheath by which the blade is formed is made intoan integral unit by bonding, i.e. by having a film of a suitable bondingagent interposed between the surfaces of the components, whereafter theresulting assembly is cured according to the selected bonding agent.

As can be readily appreciated from the above description, sharp changesin the sections of the blade are avoided by the present invention.Moreover, the present blade is not in need of struttings or bracingssince the root of the blade is integral with the metal load bearing ribstructure thereof and forms a firm rigid assembly.

Finally, it is also possible to obtain blades of different length andwidth by merely using different numbers, shapes and arrangements ofcomponents, without departing from the spirit and scope of theinvention, as defined in the appended claims.

I claim:

1. A helicopter blade for connection directly to a rotor having a hub,said blade comprising in combination, a plurality of bonded componentsforming a unitary blade structure having (A) a longitudinally extendingportion;

(B) a gradual transitional portion; and

(C) a hollow tube-like portion;

(a) said longitudinally extending portion having a metal rib componentformed of a tapered rounded leading edge projection from a verticallydisposed integral partition wall, said rounded leading edge andpartition wall defining a hollow internal structure for said rib, anouter plastic fiber cover originating near upper and lower surfaces ofthe partition wall and terminating as a trailing edge of the bladestructure, a metallic member disposed within the outer plastic fibercover at the trailing edge and parallel to said partition wall, ahoneycomb plastic filling element having an end surface adjacent saidmetallic member and an opposite end surface contacting panel membersdisposed along inner upper and inner lower surfaces of the outer plasticfiber cover, said .panel members formed of lightweight honeycomb plasticand positioned to contact the partition wall defining therewith a hollowcentral blade portion;

(b) said gradual transitional portion having a forward portioncontinuous with the leading edge tapering toward the trailing edge andjoining a forward surface of the root portion; a tapering partition wallcontinuous with the partition wall of the said extending portion,tapering toward the trailing edge and terminating near a rear surface ofthe root portion; a tapering metallic member continuous with themetallic member of said extending portion, tapering toward the leadingedge and terminating near the rear surface of the root portion forming aV configuration with the tapering partition wall; and a taperinghoneycomb plastic filling element continuous with said filling elementof the extending portion and having a terminal part filling the said Vconfiguration; and

(c) securing means disposed relative to the hollow root portion forconnecting the blade to a rotor.

2. The blade of claim 1 wherein said rib forms the major structuralsupport for said blade.

3. The blade of claim l wherein said partition wall 75 has a wallthickness of between 0.118" and 0.157".

6 4/ 1954 Pullin et al. 416-226 4/ 1962 Hinds 416-226 X 9/ 1970 Duttonet al. 416--226 6/ 1960 Jovanovich 416-226 FOREIGN PATENTS 3 195 7Australia 416-229 EVERETTE A. POWELL, JR., Primary Examiner U.S. C1.X.R.

